Cystine-containing peptides, protein

The absorption spectra of several cystine-containing peptides as obtained by Otey and Greenstein (1954) are shown in Fig. 3. Some nonadditivity of absorptivities is evident for example, the spectrum of l-cystinyl-L-cystine is obviously not simply the sum of 2 cystine spectra, even at wavelengths greater than 2500 A, where the disulfide group is the only significant chromophore. The question, What is a suitable model for cystine absorptivity in a protein is apparently farther from a satisfactory answer than is the parallel question for aromatic amino acid residues. 

Carbon-bonded sulfur compounds. These are primarily sulfur-containing peptides, proteins, and amino acids such as cysteine, cystine, and methionine. Approximately 41% of the total sulfur in soil organic matter is present in this form. 

P, J. Milburn, Y. C. Meinwald, S. Takahashi, T. Ooi, and H. A. Scheraga. Int. /. Pept. Protein Res., 31, 311 (1988). Erratum ibid., 31, 587 (1988). Chain Reversals in Model Peptides Studies of Cystine-Containing Cyclic Peptides. II. Effects of Valyl Residues and Possible / -to-(< + 3) Attractive Ionic Interactions on Cyclization of [Cys1], [Cys ] Hexapeptides. 

The high growth temperatures of archaeal thermophiles raise questions not only about the stability of the protein conformation but also about the protection of the peptide chain from covalent damage which occurs in mesophilic proteins. As shown by several authors [22-28] these chemical modifications mainly comprise, (a) deamidation of Asn and, to a minor extent. Gin (b) hydrolysis of Asp-containing peptide bonds (limited to the acidic pH range) and Asn-X bonds (c) destruction of cysteine and cystine residues. 

As illustrated in Fig. 1, our approach is based on the maleimide group linked to the synthetic peptide and the thiol group placed on the protein partner. For this purpose sufficient stability of the maleimide function in the course of the peptide synthesis as well as in the final deprotection and purification step is required. A detailed analysis of these critical aspects revealed full stability of the maleimide function under the normal conditions of peptide synthesis (56.57). On the other hand, thiolated carrier proteins are readily prepared by reduction of cystine-containing proteins, by mercaptosuccinylation of carrier proteins (66,67) or by the choice of natural mono- or poly-cysteine-containing proteins (68). 

We should stress here, as was pointed before (Stone et al. 1989), that whichever digestion approach is used—in solution, in gel, or on membrane—reduction of cystine without subsequent alkylation results in incomplete digestion leading to peptide loss. The difference is especially great for proteins such as BSA which contains 6% cysteine residues. Thus, for best peptide yield from unknown proteins, we recommend alkylation before resolving the proteins by SDS-PAGE or HPLC and before digestion. 

The thermal stability of thermolysin, a peptidase from the thermo-phillic bacterium Bacillus thermoproteolyticus, is apparently conferred by calcium bound to the enzyme (194), which has a molecular weight of 35,000 (195), and binds one mole of zinc (195) and three moles of calcium per mole of protein (196). Thermolysin contains no non-protein constituents (197) and consists of a single peptide chain containing neither cysteine nor cystine (197). Thermolysin has a high content of aspartic... 

Val-Cys-Ser-Leu-Tyr-Gln-Leu-Glu-Asn-Tyr-Cys-Asn-COO-. When only the composition is known (i.e., the sequence is unknown), the amino acids are separated by commas and enclosed in parentheses, for example, (Ala,Cys2,Gly) means a peptide containing one Ala, two Cys, and one Gly in an unknown order. A "polypeptide chain" is, by convention, a continuous chain linked only by peptide bonds. A protein may have only one polypeptide chain and then the polypeptide and the protein are synonymous. In other cases, a protein may have more than one polypeptide chain, as does insulin. In such cases, the different peptide chains within a protein may be held together by noncovalent forces, as in the case of hemoglobin, sometimes supplemented by covalent cystine cross links, as in the case of insulin. In many cases, the noncovalent interactions allow more than one conformation and a protein may switch from one conformation to another as part of its function. 

Isozymes from Drosophila melanogaster have been purified (581,588). Somewhat different molecular weights of the protein have been deduced, but the value is likely to be close to 50,000 (514,518,581-583). The genetic analyses strongly indicate that the enzyme is a dimer. A subunit molecular weight close to 25,000 has been determined (518), although lower, unlikely values have also been reported (583). The number of tryptic peptides analyzed by peptide mapping (518) is also consistent with an enzyme molecule composed of two identical subunits. Amino acid compositions (518,588) show that the protein contains no methionine and only small amounts of half-cystine and tryptophan. 

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